Channel access indication method and device to avoid unnecessary probe delay

ABSTRACT

A channel access indication method and device. The method includes: receiving, by a first communications device, a channel synchronization request sent by a second communications device, where the channel synchronization request is used to request the first communications device to send a synchronization frame to the second communications device, and a wake-up receiver is configured for the second communications device; and according to the channel synchronization request and a time at which the second communications device is woken up and that is learned by the first communications device based on preset signaling, sending, by the first communications device when a channel is idle, the synchronization frame to the woken-up second communications device, where the synchronization frame is used to instruct the woken-up second communications device to access the channel after receiving the synchronization frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2018/076999, filed on Feb. 23, 2018, which claims priority toChinese Patent Application No. 201710179619.7, filed on Mar. 23, 2017.The disclosures of the aforementioned applications are incorporatedherein by reference in their entireties.

FIELD

This application relates to communications technologies, and inparticular, to a channel access indication method and device.

BACKGROUND

In a wireless fidelity (WiFi) network, a receiving device wastes aconsiderable amount of energy listening when no signal is to be received(idle listening). In other words, if a station STA continuously listenson a channel when no message is to be sent or received, a large amountof energy is consumed. Therefore, a sleep mechanism is introduced in acommunications standard, so that the station can enter a deep sleepstate when no data is to be sent or received, to reduce energyconsumption caused by continuous listening. However, when the station isin deep sleep, an access point (AP) cannot communicate with the station,and transmission between the AP and the station can be performed onlyafter the station wakes up. This may cause latency. To avoid a highlatency caused by the sleep mechanism, the station usually wakes upperiodically according to a sleep policy to check whether there is datato be received, but this reduces sleep efficiency of the station.

Therefore, in addition to optimizing the sleep policy, another technicalapproach to reduce energy wasted by the device in idle listening is touse a wake-up receiver (WUR). A core idea of the technical approach isas follows: In addition to a legacy 802.11 main transceiver module, alow power WUR is added to the receiving device. The legacy 802.11transceiver module is an 802.11 main radio (MR) or main transceiver, asshown in FIG. 1. After the 802.11 MR enters deep sleep, the low powerWUR wakes up and starts to work. If the AP needs to communicate with astation that has a WUR and an 802.11 MR, the AP first sends a wake-upframe (or wake up packet, WUP) to the WUR; the WUR wakes up the 802.11MR of the station after correctly receiving the WUP sent to the WUR; andthen the AP communicates with the 802.11 MR that wakes up. Aftercompleting communication with the AP, the 802.11 MR goes to sleep again.At the same time, the WUR starts to detect again whether there is a WUPto be sent to the WUR, to wake up the 802.11 MR again. In thistechnology, the low power WUR instead of the 802.11 MR is used to listenon a channel when a medium is idle, thereby effectively reducing energywasted when the device performs listening.

The MR of the station equipped with the WUR belongs to a legacy 802.11device, and usually needs to satisfy an energy-saving mechanismspecified in the 802.11 protocol. One stipulation is that, when wakingup, the MR of the station needs to wait for a probe delay time or listento a frame carrying a field used to update a network allocation vector(NAV) of a non-target station, and then the MR of the station can startto perform clear channel assessment (CCA), and actively preempt oraccess a channel to send a data packet to the AP. Therefore, when wakingup, the MR of the station does not directly preempt a channel to senddata, so that a collision with ongoing communication between a hiddennode and the AP is avoided.

However, after waking up, the MR of the station waits an excessivelylong probe delay time to access the channel. As a result, powerconsumption of the station is relatively large.

SUMMARY

A channel access indication method and device is provided to resolve atechnical problem in the prior art that power consumption of a stationis relatively large because after waking up, an MR of the station waitsan excessively long probe delay time to access a channel.

A first exemplary embodiment provides a channel access indicationmethod, including:

receiving, by a first communications device, a channel synchronizationrequest sent by a second communications device, where the channelsynchronization request is used to request the first communicationsdevice to send a synchronization frame to the second communicationsdevice, and a WUR is configured for the second communications device;and according to the channel synchronization request and a time at whichthe second communications device is woken up and that is learned by thefirst communications device based on preset signaling, sending, by thefirst communications device when a channel is idle, the synchronizationframe to the woken-up second communications device, where thesynchronization frame is used to instruct the woken-up secondcommunications device to access the channel after receiving thesynchronization frame.

According to the channel access indication method provided in anembodiment, the second communications device sends the channelsynchronization request to the first communications device, to requestthe first communications device to assist the second communicationsdevice in quickly accessing the channel. Therefore, after receiving thechannel synchronization request and determining, based on the learnedtime at which the second communications device is woken up, that thesecond communications device has woken up and that the channel is idle,the first communications device sends the synchronization frame to thesecond communications device, to trigger the second communicationsdevice to access the channel without waiting for a probe delay time.This greatly shortens a waiting time of an MR of the secondcommunications device, and reduces power consumption overheads of thesecond communications device caused by waiting.

In a possible embodiment, there are a plurality of woken-up secondcommunications devices, and the sending, when a channel is idle, thesynchronization frame to the woken-up second communications deviceincludes:

sending, by the first communications device when the channel is idle, afirst synchronization frame to any one of the number of woken-up secondcommunications devices, where the first synchronization frame carries anidentifier of the any one woken-up second communications device; and thefirst synchronization frame is used to instruct the any one woken-upsecond communications device to wait a first preset duration to accessthe channel after receiving the first synchronization frame. Optionally,the first synchronization frame may be a clear-to-send (CTS) frame, arequest-to-send (RTS) frame, or a trigger frame.

In a possible embodiment, there are a number of woken-up secondcommunications devices, and the sending, when a channel is idle, thesynchronization frame to the woken-up second communications deviceincludes:

sending, by the first communications device when the channel is idle, asecond synchronization frame to the number of woken-up secondcommunications devices, where the second synchronization frame is usedto instruct each woken-up second communications device to wait a secondpreset duration to perform a backoff procedure to contend for access tothe channel after receiving the second synchronization frame; and areceiver address of the second synchronization frame is a broadcastaddress. The receiver address of the second synchronization frame is thebroadcast address. Optionally, the second synchronization frame may be aCTS frame, an RTS frame, or a contention free end (CF-end) frame.

With reference to the foregoing embodiments, the CTS frame may carrysecond indication information; and the second indication information isused to indicate, to the woken-up second communications device, that theCTS frame is a synchronization frame.

In a possible embodiment, there are a number of woken-up secondcommunications devices, and the sending, when a channel is idle, thesynchronization frame to the woken-up second communications deviceincludes:

sending, by the first communications device when the channel is idle, athird synchronization frame to the number of woken-up secondcommunications devices, where the third synchronization frame carries asub-channel resource indication of each woken-up second communicationsdevice and an identifier of each woken-up second communications device;a receiver address of the third synchronization frame is a broadcastaddress; and the third synchronization frame is used to instruct thenumber of woken-up second communications devices to wait a first presetduration to simultaneously access the channel based on their respectivesub-channel resource indications after receiving the thirdsynchronization frame. Optionally, the third synchronization frame maybe a multi-user CTS frame, a multi-user RTS frame, or a trigger frame.

In a possible embodiment, there are a number of woken-up secondcommunications devices, and the sending, when a channel is idle, thesynchronization frame to the woken-up second communications deviceincludes:

sending, by the first communications device when the channel is idle, aphysical layer legacy preamble (L-preamble) to the number of woken-upsecond communications devices, where the L-preamble carries firstindication information and all or a portion of bits of a check codefield of a WUP that is received by WURs of the number of woken-up secondcommunications devices to wake up main transceivers of the number ofsecond communications devices; the first indication information is usedto indicate, to the number of woken-up second communications devices,that the L-preamble is a synchronization frame; the all or the portionof bits of the check code field are used to indicate identifiers of thenumber of woken-up second communications devices; and

the L-preamble is used to instruct the number of woken-up secondcommunications devices to wait a second preset duration to perform abackoff procedure to contend for access to the channel after receivingthe L-preamble.

In a possible embodiment, if there is one woken-up second communicationsdevice, the synchronization frame is an L-preamble, where the L-preamblecarries first indication information and all or a portion of bits of acheck code field of a WUP received by a WUR of the woken-up secondcommunications device; the first indication information is used toindicate, to the second communications device, that the L-preamble is asynchronization frame; and the all or the portion of bits of the checkcode field are used to indicate an identifier of the woken-up secondcommunications device.

Optionally, if there is one woken-up second communications device, thesynchronization frame may be a CTS frame, an RTS frame, or a triggerframe; and the synchronization frame carries an identifier of thewoken-up second communications device.

In a possible embodiment, the receiving, by a first communicationsdevice, a channel synchronization request sent by a secondcommunications device includes:

receiving, by the first communications device, an association requestframe sent by the second communications device, where the associationrequest frame carries indication information of the channelsynchronization request of the second communications device.

In a possible embodiment, the receiving, by a first communicationsdevice, a channel synchronization request sent by a secondcommunications device includes:

receiving, by the first communications device, a management frame or acontrol frame sent by the second communications device, where themanagement frame or the control frame carries indication information ofthe channel synchronization request.

In conclusion, regardless of a single-device wake-up scenario or amulti-device wake-up scenario, provided that the second communicationsdevice sends the channel synchronization request to the firstcommunications device before the second communications device goes tosleep, the first communications device sends, when the channel is idleand with reference to the time at which the second communications deviceis woken up and that is learned by the first communications device, thesynchronization frame to the woken-up second communications device totrigger the woken-up second communications device to access the channelwithout waiting for the probe delay time, thereby reducing the waitingtime of the MR of the woken-up second communications device, andreducing power consumption of the second communications device. Inaddition, the first communications device sends the firstsynchronization frame to any one of the woken-up second communicationsdevices, to trigger the second communications devices to access thechannel without waiting for the probe delay time. This greatly reducesthe transmission time of the synchronization frame, and also ensuresthat the woken-up second communications devices can quickly access thechannel.

According to a second exemplary embodiment, to implement the channelaccess indication method, an embodiment provides a channel accessindication device. The device may be the first communications device,and the first communications device may be a station or an AP. Thedevice has a function of implementing the channel access indicationmethod. The function may be implemented by hardware, or may beimplemented by hardware executing corresponding software. The hardwareor the software includes one or more modules corresponding to thefunction.

In a possible implementation of the second exemplary embodiment, thechannel access indication device includes a number of function modulesor units, configured to implement any channel access indication method.

In another possible implementation of this embodiment, a structure ofthe channel access indication device may include a processor, areceiver, and a transmitter (or a transceiver). The processor isconfigured to support the device in performing a corresponding functionin any channel access indication method. The transceiver is configuredto support communication between the device and another network deviceor terminal device. For example, the transceiver may be a correspondingradio frequency module or baseband module. The device may furtherinclude a memory. The memory is configured to be coupled to theprocessor, and stores a program instruction and data that is necessaryfor the channel access indication device to perform the channel accessindication method.

A third exemplary embodiment provides a computer storage medium,configured to store computer software instructions used by the channelaccess indication device, where the computer software instructionsinclude a program designed to execute the first embodiment.

A fourth exemplary embodiment provides a computer program product, wherethe computer program product includes an instruction, and when thecomputer program is executed by a computer, the instruction enables thecomputer to perform a function performed by the first communicationsdevice in the foregoing method.

Compared with the prior art, according to the channel access indicationmethod and device, the second communications device sends the channelsynchronization request to the first communications device, to requestthe first communications device to assist the second communicationsdevice in quickly accessing the channel. Therefore, after receiving thechannel synchronization request and determining, based on the learnedtime at which the second communications device is woken up, that thesecond communications device has woken up and that the channel is idle,the first communications device sends the synchronization frame to thesecond communications device, to trigger the second communicationsdevice to access the channel without waiting for the probe delay time.This greatly shortens the waiting time of the MR of the secondcommunications device, and reduces the power consumption overheads ofthe second communications device caused by waiting.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic structural diagram of a station equipped with awake-up receiver;

FIG. 2 is a schematic structural diagram of a WLAN system;

FIG. 3 is a schematic diagram of channel access when a hidden stationsends data;

FIG. 4 is a schematic diagram of channel access when a hidden stationdoes not send data;

FIG. 5 is a schematic flowchart of an embodiment of a channel accessindication method;

FIG. 6 is a schematic diagram of channel access triggered by asynchronization frame;

FIG. 7 is a schematic diagram of channel access in a single-devicewake-up scenario;

FIG. 8 is a schematic diagram of channel access in a multi-devicewake-up scenario;

FIG. 9 is a schematic structural diagram of an embodiment of a channelaccess indication apparatus; and

FIG. 10 is a schematic structural diagram of an embodiment of a channelaccess indication device.

DESCRIPTION OF EMBODIMENTS

Embodiments described herein may be applied to a wireless local areanetwork (WLAN). Currently, standards used by the WLAN are the Instituteof Electrical and Electronics Engineers (IEEE) 802.11 family. A stationand an AP are basic components of the WLAN.

The AP is an access point used by a mobile user to access a wirednetwork, and is mainly deployed within a home, a building, and a campus,with a typical coverage radius of a few dozen meters to a few hundredmeters. The AP may also be deployed outdoors. The AP is equivalent to abridge that connects a wired network and a wireless network. A mainfunction of the AP is to connect wireless network clients together, andthen connect the wireless network to the ethernet. The AP may be aterminal device or a network device with a WiFi chip. Optionally, the APmay be a device that supports the 802.11ax standard. Further,optionally, the AP may be a device that supports a number of WLANstandards such as 802.11ac, 802.11n, 802.11g, 802.11b, and 802.11a. Inthe embodiments, a type of a standard supported by the AP is notlimited.

The station is generally a client device in the WLAN. The station may bemobile or fixed and is a basic component of the WLAN. The station may bea wireless communications chip, a wireless sensor, or a wirelesscommunications terminal, for example, a mobile phone supporting a WiFicommunication function, a tablet computer supporting a WiFicommunication function, a set-top box supporting a WiFi communicationfunction, a smart television supporting a WiFi communication function, asmart wearable device supporting a WiFi communication function, avehicle-mounted communications device supporting a WiFi communicationfunction, or a computer supporting a WiFi communication function.

FIG. 2 is a schematic structural diagram of a WLAN system. As shown inFIG. 2, one AP in the WLAN system may exchange information with multiplestations (for example, three stations in FIG. 2), including STA 1, STA2, and STA 3. This is not limited thereto. Alternatively, one AP mayexchange information with one or more station groups, and the stationsmay also interact with each other.

It should be noted that an 802.11 main radio (MR) (or a maintransceiver) and a WUR may be configured for both a first communicationsdevice and a second communications device; or a main transceiver may beconfigured for a first communications device, and a main transceiver anda WUR may be configured for a second communications device. For thefirst communications device and the second communications device, referto the structure shown in FIG. 1. The first communications device may bean AP or a station, and the second communications device may be astation or an AP. When the first communications device is an AP, thesecond communications device is a station; or when the firstcommunications device is a station, the second communications device isan AP. The following embodiments are all described by using an examplein which the first communications device is an AP, and the secondcommunications device is a station.

Generally, wake-up of an MR includes active wake-up and passive wake-up.The passive wake-up of the MR is discussed, and a process of the passivewake-up may be as follows: An AP sends a WUP to at least one stationassociated with the AP, where the WUP may be used to indicate receptionparameters of an MR of the at least one station after the MR is woken upfrom a sleep state, for example, a receive mode indication and anindication of a time at which the MR is woken up. A WUR wakes up the MRof the station after receiving the WUP sent by the AP. After the MR ofthe station is woken up, the MR sends a power save poll (PS-Poll) frameor an acknowledgment frame to the AP to notify the AP that the MR iswoken up. Then, the AP returns an acknowledgment response, or directlytransmits data to the MR of the station. Optionally, the AP may directlysend a data frame to the MR of the station after the MR of the stationis woken up, without waiting for the MR of the station to send a PS-Pollframe; or the AP may send an RTS frame to the MR of a woken-up station,and then the MR of the station sends a CTS frame to the AP. In addition,the AP may send a WUP to a non-AP station, or a non-AP station may senda WUP to the AP. This is not limited by this embodiment.

The MR of the station equipped with the WUR belongs to a legacy 802.11device, and usually needs to satisfy an energy-saving mechanismspecified in the 802.11 protocol. One stipulation is that, when wakingup, the MR of the station needs to wait for a probe delay time or listento a frame carrying a field used to update a NAV of a non-targetstation, and then the MR of the station can start to perform CCA, andactively preempt a channel (in other words, access the channel) to senda data packet to the AP. Therefore, when waking up, the MR of thestation does not directly preempt a channel to send data, so that acollision with ongoing communication between a hidden node and the AP isavoided. For example, as shown in FIG. 3, a station 1 and a station 2are mutually hidden nodes. The station 1 and the station 2 cannot detecta data packet sent by each other. If an MR of the station 2 sends datato an AP within a probe delay when waking up, sending of the data by thestation 2 interferes with receiving of data of the station 1 by the AP.If the station 1 and the station 2 are not mutually hidden nodes, andthe MR of the station 2 detects that the station 1 is sending data, theMR of the station 2 does not preempt a channel to send data, and thecollision mentioned above does not occur. Therefore, in this case, toavoid a collision between sending of data by a station after the stationwakes up and communication of a hidden node, the station waits for aprobe delay time when waking up (FIG. 3 shows a case in which afterwaking up, the station 2 waits a probe delay time to send data, to avoida collision with sending of the data by the station 1). The time isequal to a sum of a longest physical layer convergence procedureprotocol data unit (PPDU) transmission time, a short inter-frame space(SIFS), and a transmission time of an acknowledgment frame.

However, in the foregoing mechanism in which the MR waits after wakingup, there may be a case where an MR of a station is in a waiting stateafter waking up, another hidden station actually does not perform datatransmission with the AP. As shown in FIG. 4, a hidden station (namely,a station 1) of a station 2 is not sending data. In this case, a waitingprocess of the station 2 wastes a great amount of energy of the station2, and power consumption of the station 2 is relatively large. For astation equipped with a button cell (for example, a sensor equipped witha button cell), the station has an extremely strict requirement forpower consumption, and the button cell is expected to work for more thanone year. If an MR of a station of this type still blindly waits for aprobe delay time after waking up, and then preempts a channel to senddata, a quantity of electricity of the station is consumed. This isextremely not conducive to energy conservation.

Therefore, the channel access indication method and device provided areintended to resolve a technical problem in the prior art that powerconsumption of a station is relatively large because after waking up, anMR of the station blindly waits an excessively long probe delay time toaccess a channel.

It should be understood that, although terms such as “first”, “second”,and “third” may be used in the embodiments to describe various elementsor embodiments, the various elements or embodiments should not belimited to these terms. These terms are merely used to distinguish theelements or embodiments from one another. For example, without departingfrom the scope of the embodiments, a first elements or embodiments mayalso be referred to as a second elements or embodiments, and similarly,a second elements or embodiments may also be referred to as a firstelements or embodiments.

The following describes technical solutions in detail by using exemplaryembodiments. The following exemplary embodiments may be combined witheach other, and similar concepts or processes may not be repeatedlydescribed in some embodiments.

FIG. 5 is a schematic flowchart of an embodiment of a channel accessindication method. This embodiment relates to the following process: Toshorten a waiting time of a second communications device after thesecond communications device wakes up, the second communications devicesends a channel synchronization request to a first communicationsdevice, so that the first communications device can send, with referenceto a learned time at which the second communications device is woken up,a synchronization frame to the woken-up second communications device,and then the second communications device can determine, based on thesynchronization frame, to access a channel without waiting for a probedelay time. As shown in FIG. 5, the method includes the following steps.

In step S101, the first communications device receives the channelsynchronization request sent by the second communications device, wherethe channel synchronization request is used to request the firstcommunications device to send the synchronization frame to the secondcommunications device.

A WUR is configured for the second communications device.

To reduce power consumption, the second communications device sends thechannel synchronization request to the first communications devicebefore the second communications device goes to sleep, where the channelsynchronization request is used to request the first communicationsdevice to send the synchronization frame to the second communicationsdevice. The first communications device may return a synchronizationresponse frame to the second communications device after receiving thechannel synchronization request. It should be noted that, the channelsynchronization request may be used to explicitly request the firstcommunications device to send the synchronization frame. For example,the channel synchronization request directly notifies the firstcommunications device that there is a need to obtain the synchronizationframe of the first communications device, so that the firstcommunications device can assist the second communications device inquickly accessing the channel after the second communications device iswoken up. Optionally, the channel synchronization request mayalternatively be used to implicitly request the first communicationsdevice to send the synchronization frame. For example, the channelsynchronization request may carry power consumption information of thesecond communications device, to notify the first communications devicethat the second communications device has a relatively strictrequirement for power consumption, and the first communications deviceis required to send the synchronization frame to assist the secondcommunications device in accessing the channel without waiting for theprobe delay time after an MR is woken up. A form of the channelsynchronization request is not limited in this embodiment.

Optionally, that the first communications device receives the channelsynchronization request sent by the second communications device mayinclude the following several implementations.

In a first implementation, the first communications device receives anassociation request frame sent by the second communications device,where the association request frame carries indication information ofthe channel synchronization request of the second communications device.

In this implementation, in a phase in which the second communicationsdevice performs association with the first communications device, thesecond communications device sends the association request frame to thefirst communications device, to send the channel synchronization requestto the first communications device. The association request framecarries the indication information of the channel synchronizationrequest of the second communications device. Optionally, the indicationinformation may be explicit indication information, or may be implicitpower consumption information of the second communications device.

In a second embodiment, the first communications device receives amanagement frame or a control frame sent by the second communicationsdevice. Optionally, the second communications device may send themanagement frame or the control frame to the first communications devicewhen a quantity of electricity of the second communications device isless than a preset electricity quantity threshold. The management frameor the control frame carries indication information of the channelsynchronization request. Optionally, if the first communications devicesends the management frame, the indication information may be asynchronization request element in the management frame. Optionally, theindication information of the channel synchronization request mayalternatively be carried in a field in a data frame.

In step S102, according to the channel synchronization request and atime at which the second communications device is woken up and that islearned by the first communications device based on preset signaling,the first communications device sends, when the channel is idle, thesynchronization frame to a woken-up second communications device, wherethe synchronization frame is used to instruct the woken-up secondcommunications device to access the channel after receiving thesynchronization frame.

In a phase, an MR of the second communications device enters a sleepstate. If the first communications device needs to communicate with theMR of the second communications device, for example, send downlink datato the MR of the second communications device, the first communicationsdevice may send a WUP to the WUR of the second communications device, towake up the MR of the second communications device. After receiving theWUP the WUR of the second communications device triggers a maintransceiver of the second communications device to wake up. Optionally,the WUP may carry a wake-up moment of the WUR of the secondcommunications device, to instruct the WUR of the second communicationsdevice to wake up at the specified wake-up moment.

The first communications device may learn, based on the presetsignaling, the time at which the second communications device is wokenup. Optionally, the preset signaling may be the WUP. When the WUPcarries the wake-up moment of the WUR of the second communicationsdevice, the first communications device may learn, based on the WUP sentby the first communications device to the second communications device,the time at which the second communications device is woken up.Optionally, when the WUP does not carry the wake-up moment of the WUR ofthe second communications device, the first communications device mayestimate, by using a sending moment of the WUP, the time at which thesecond communications device is woken up. Optionally, the presetsignaling may be other information. This is not limited in thisembodiment. The wake-up moment of the second communications device maybe a moment specified by the first communications device, or may be anestimated wake-up time. After the first communications devicedetermines, based on the time at which the second communications deviceis woken up, that the second communications device has woken up (herein,the determined moment at which the second communications device wakes upis not notified by the woken-up second communications device to thefirst communications device, but is estimated or specified by the firstcommunications device), in a period in which the second communicationsdevice is awake, the first communications device detects whether thechannel is idle.

When the first communications device detects that the channel is idle,the first communications device sends the synchronization frame to thesecond communications device that needs to be assisted in quicklyaccessing the channel. In other words, the first communications devicesends the synchronization frame to the second communications device thatpreviously sends the channel synchronization request to the firstcommunications device. After the second communications device receivesthe synchronization frame, the second communications device may learn acurrent channel status. Therefore, the second communications device istriggered by the synchronization frame to access the channel.Optionally, a manner of accessing the channel may be that the secondcommunications device sends a wake-up report frame to the firstcommunications device. The wake-up report frame may be an acknowledgmentframe or a PS-poll frame, or may be a CTS frame. Any type of the wake-upreport frame may be implemented. After the first communications devicereceives the wake-up report frame sent by the second communicationsdevice, the first communications device may send an acknowledgment framerespond to the second communications device or directly send downlinkdata to the second communications device.

Optionally, that the second communications device accesses the channelafter receiving the synchronization frame may be that the secondcommunications device directly accesses the channel after receiving thesynchronization frame, or may be that the second communications devicewaits a preset duration to access the channel after receiving thesynchronization frame. The preset duration may be a short inter-framespace (SIFS, SIFS duration, or SIFS time), or may be a distributedcoordination function inter-frame space (DIFS), or may be otherduration, provided that the preset duration is less than the probe delaytime. For example, as shown in FIG. 6, when an AP learns that a station2 wakes up, and the AP detects that a channel is idle, the AP may send asynchronization frame to the woken-up station 2. After receiving thesynchronization frame, the station 2 waits an SIFS time, and then mayimmediately respond with a PS-poll frame to notify the AP that thestation 2 has woken up. Then, the AP sends an acknowledgment frame ordirectly sends downlink data to the station 2.

Optionally, in a period in which the first communications devicedetermines, based on the learned time at which the second communicationsdevice is woken up, that the second communications device has woken up,if the first communications device detects that the channel is in a busystate, the first communications device does not perform any operation.When the channel is idle, and the first communications device does notyet receive a wake-up report frame of the second communications device,the first communications device continues to send the synchronizationframe to the second communications device, to assist the secondcommunications device in quickly accessing the channel.

Optionally, the synchronization frame may be a frame for one woken-upsecond communications device to quickly access a channel, for example,referring to the example shown in FIG. 6. Alternatively, thesynchronization frame may be a frame for a number of woken-up secondcommunications devices to quickly access a channel. This exemplaryembodiment is not meant to limit the number of additional communicationsdevices.

Optionally, in this embodiment, based on the time at which the secondcommunications device is woken up and that is learned by the firstcommunications device, the first communications device may also detect,in a period in which the second communications device is awake, whetherthe channel is idle, and directly send the synchronization frame to thesecond communications device when detecting that the channel is idle.Additionally, the second communications device may not need to send thechannel synchronization request to the first communications device, orthe first communications device does not need to wait until the secondcommunications device sends the channel synchronization request, to sendthe synchronization frame to the second communications device.

It can be understood that, after being woken up, the MR of the secondcommunications device may access the channel, without waiting for theprobe delay time after receiving the synchronization frame sent by thefirst communications device. Therefore, a waiting time of the MR of thesecond communications device is greatly shortened, and power consumptionoverheads of the second communications device caused by waiting arereduced.

According to the channel access indication method, the secondcommunications device sends the channel synchronization request to thefirst communications device, to request the first communications deviceto assist the second communications device in quickly accessing thechannel. Therefore, after receiving the channel synchronization requestand determining, based on the learned time at which the secondcommunications device is woken up, that the second communications devicehas woken up and that the channel is idle, the first communicationsdevice sends the synchronization frame to the second communicationsdevice, to trigger the second communications device to access thechannel without waiting for the probe delay time. This greatly shortensthe waiting time of the MR of the second communications device andreduces the power consumption overheads of the second communicationsdevice caused by waiting.

With reference to the description of the foregoing embodiment, in thefollowing several implementations, exemplary implementations of theforegoing synchronization frame is described from the perspective of aframe structure.

In a first possible implementation of an exemplary embodiment, thesynchronization frame may be an L-preamble that carries first indicationinformation, and does not carry any payload part. The synchronizationframe includes a legacy short training field, a legacy long sequencefield, and a legacy signaling field. Reference is made to a physicallayer legacy 802.11 preamble shown in Table 1a. If calculation isperformed based on a minimum transmission rate that is generated bybinary phase shift keying (BPSK) modulation and a convolutional codewith a code rate of 0.5, a transmission time of the L-preamble is 20 μs.The transmission time is far less than the probe delay time. The legacysignaling field in the physical layer legacy preamble includes a 4-bitrate field, a 1-bit reserved field, a 12-bit length field, a 1-bit checkcode field, and a 6-bit tail field, as shown in Table 1.

TABLE 1 Rate Reserved Length Check code Tail

TABLE 1a

TABLE 1b

The L-preamble in this implementation carries the first indicationinformation, and the first indication information is used to indicate,to the second communications device, that the L-preamble is asynchronization frame. In this way, after receiving an L-preamble, thesecond communications device may determine whether the L-preamble is asynchronization frame, depending on whether the L-preamble carries thefirst indication information. Optionally, the first indicationinformation may be implemented by using the length field of theL-preamble. For example, all 12 bits of the length field are set tozeros. Optionally, the first indication information may alternatively beimplemented by using a reserved bit of the L-preamble. The reserved bitof the L-preamble is set to 1, and it may indicate that the L-preambleis a synchronization frame. Optionally, the first indication informationmay alternatively be implemented by using the rate field of theL-preamble. Only eight values of the 4-bit rate field are used in acurrent protocol. For the eight values, refer to the following Table 2.In this implementation, it may be determined, by setting the 4-bit ratefield to another value, that the L-preamble sent to the secondcommunications device is a synchronization frame. For example, the ratefield is set to 1111, and 1111 is the first indication information.

TABLE 2 Rate field 1101 0111 0101 0111 1001 1011 0001 0011 Rate Mb/s (206 9 12 18 24 36 48 54 MHz channels)

An L-preamble in the current protocol does not carry a receiver address.Therefore, to further determine a second communications device to whichthe synchronization frame is sent, it is proposed in this implementationthat the L-preamble carries indirect address information that canidentify the second communications device. The indirect addressinformation may be all or a portion of bits of a check code field,carried by a rate field, of a WUP of the second communications device.For example, the some bits may be four bits such as four leastsignificant bits in a cyclic redundancy check (CRC) code field or aframe check sequence (FCS) field. A check code field or an FCS fieldcorresponds to a WUP. Different WUPs have different check code fields orframe check sequence fields, and the different WUPs are in a one-to-onecorrespondence with identifiers of different second communicationsdevices. Therefore, different woken-up second communications devices maybe distinguished by using different bits of the check code fields.

In conclusion, in this implementation, the synchronization frame may bethe L-preamble, and the L-preamble carries the first indicationinformation and all or a portion of bits of a check code field of theWUP received by the WUR of the second communications device. Afterreceiving the L-preamble, the second communications device may identify,by using the first indication information, that the L-preamble is thesynchronization frame sent by the first communications device, andidentify, by using all or a portion of bits of the check code field,carried in the L-preamble of the WUP, whether the synchronization frameis the synchronization frame sent to the second communications device.

Optionally, the synchronization frame may alternatively be anotherspecial L-preamble. The synchronization frame includes a legacy shorttraining field, a legacy long sequence field, a legacy signaling field,and an orthogonal frequency division multiplexing (OFDM) symbolmodulated via binary phase shift keying (BPSK). The OFDM symbolmodulated via BPSK may be a product of a repeated legacy signaling fieldin the L-preamble and a specified random sequence (which is not allones). For example, the random sequence may be all minus ones.Alternatively, the OFDM symbol modulated by using BPSK may be a new OFDMsymbol modulated by using BPSK. The OFDM symbol may carry 24-bitinformation (the OFDM is modulated by using BPSK and encoded by using aconvolutional code with a code rate of 0.5). For example, the OFDMsymbol may carry the first indication information and all or a portionof bits of a check bit of a WUP. Optionally, for a structure of thesynchronization frame, refer to the following Table 2a and Table 2b.

TABLE 2a

TABLE 2b

In a second possible implementation of an embodiment, thesynchronization frame may be a CTS frame. For a frame structure of theCTS frame, refer to the following Table 3. If calculation is performedbased on a minimum transmission rate, considering that a physical layerpreamble of a CTS frame is a L-preamble, a transmission time of the CTSframe that is transmitted as the synchronization frame is approximately40 μs. The transmission time is short and less than the probe delaytime.

TABLE 3 Frame control Duration field Receiver address field Frame checkfield (2 bytes) (6 bytes) sequence field (2 bytes) (4 bytes)

Optionally, the CTS frame may not carry second indication information.Provided that a CTS frame is sent, after the first communications devicereceives the channel synchronization request of the secondcommunications device, and the MR of the second communications devicewakes up, by the first communications device according to the channelsynchronization request, the CTS frame is the synchronization frame sentby the first communications device. Optionally, the CTS frame may carrysecond indication information, and the second indication information isused to explicitly indicate, to the woken-up second communicationsdevice, that the CTS frame is a synchronization frame. The secondindication information may be indicated by using a field (or a bit) inthe CTS frame. For example, the duration field may be set to 0 (whichindicates the second indication information), and the woken-up secondcommunications device may identify the CTS frame as a synchronizationframe.

In a third possible implementation of an embodiment, the foregoingsynchronization frame may be an RTS frame. For a frame structure of theRTS frame, refer to the following Table 4. The RTS frame may carrysecond indication information used to indicate, to the woken-up secondcommunications device, that the RTS frame is a synchronization frame.For example, the second indication information may be implemented byusing a duration field in the following Table 4. When the duration fieldis set to 0, it represents that a current RTS frame is a synchronizationframe. If calculation is performed based on a minimum transmission rate,considering that a physical layer preamble of an RTS frame is aL-preamble, a transmission time of the RTS frame is approximately 47 μs.The transmission time is less than the probe delay time.

TABLE 4 Frame control Duration Receiver Transmitter Frame check fieldfield address field address field sequence field (2 bytes) (2 bytes) (6bytes) (6 bytes) (4 bytes)

It should be noted that, in the third possible implementation, anRTS/CTS exchange procedure is used. However, in this case, a conditionfor using RTS/CTS is no longer that a length of a subsequentlytransmitted data packet, or time reaches a threshold, but that the maintransceiver of the woken-up second communications device sends channelsynchronization request information to an AP.

In a fourth possible implementation of an embodiment, the foregoingsynchronization frame may be a CF-end frame. After the MR of the secondcommunications device wakes up, if a CF-end frame sent by the firstcommunications device is received, it is determined that thesynchronization frame sent by the first communications device isreceived. For a frame structure of the CF-end frame, refer to thefollowing Table 5. A basic service set identifier (BSSID) may be shownin Table 5. If calculation is performed based on a minimum transmissionrate, considering that a physical layer preamble of the CF-end frame isa L-preamble, a transmission time is approximately 47 μs. Thetransmission time is less than the probe delay time. A receiver addressof the CF-end frame is a broadcast address.

TABLE 5 Frame Duration Receiver address BSSID Frame check control fieldfield field field field sequence (2 bytes) (2 bytes) (6 bytes) (6 bytes)(4 bytes)

In a fifth possible implementation of an embodiment, the foregoingsynchronization frame may be a trigger frame in the 802.11ax protocol.If calculation is performed based on a minimum transmission rate,considering that a physical layer preamble of the trigger frame is anL-preamble, a transmission time is approximately 77 μs. The transmissiontime is less than the probe delay time. For a frame structure of thetrigger frame, refer to the following Table 6.

TABLE 6 Frame Duration Receiver Transmitter Common User . . . UserPadding Frame control (2 bytes) address address information informationinformation (Variable) check (2 bytes) (6 bytes) (6 bytes) (8 bytes or(5 bytes or (5 bytes or sequence more) more) more) (4 bytes)

The foregoing several possible implementations describe the exemplaryimplementations of the synchronization frame. It should be noted that,the exemplary implementations of the synchronization frame may changedepending on wake-up scenarios, and in different wake-up scenarios, thefirst communications device may send the synchronization frame indifferent manners. Actual scenarios of waking up the MR of the secondcommunications device may include single-device wake-up and multi-devicewake-up. The single-device wake-up means that the first communicationsdevice chooses to wake up an MR of only one second communicationsdevice. A WUP sent by the first communications device to a WUR of thesecond communications device carries an identifier of only one secondcommunications device. The multi-device wake-up means that a WUP sent bythe first communications device is for WURs of a number of secondcommunications devices, and the WUP is a multi-device WUP. The WUPcarries identifiers of the multiple second communications devices. Thefollowing describes, with reference to different wake-up scenarios, somechanges to the synchronization frame, sending manners of thesynchronization frame, and channel access manners corresponding todifferent sending manners of the synchronization frame.

1. A single-device wake-up scenario: In this scenario, there is onewoken-up second communications device. Before an MR of the secondcommunications device goes to sleep, the second communications devicesends a channel synchronization request to the first communicationsdevice. In a phase, the MR of the second communications device enters asleep state, and the first communications device sends a WUP to a WUR ofthe second communications device, to trigger the MR of the secondcommunications device to wake up. After the first communications devicereceives the channel synchronization request, and learns that the MR ofthe second communications device has woken up (as described above, awake-up moment herein is a time estimated or specified by the firstcommunications device, but not notified by the second communicationsdevice), the first communications device sends a synchronization frameto the MR of the single second communications device. The secondcommunications device may access a channel without waiting for a probedelay time after receiving the synchronization frame.

In this scenario, the synchronization frame may be the foregoingL-Preamble that carries first indication information and all or aportion of bits of a check code field of the WUP; or the synchronizationframe may be the foregoing CTS frame that carries second indicationinformation, where the CTS frame carries an identifier of the woken-upsecond communications device; or the synchronization frame may be theforegoing RTS frame that carries second indication information, wherethe RTS frame carries an identifier of the woken-up secondcommunications device; or the synchronization frame may be the foregoingtrigger frame, where the trigger frame carries an identifier of thewoken-up second communications device. For example, a receiver addressof the trigger frame is set to an address of the woken-up secondcommunications device. The trigger frame in Table 5 includes a userinformation field. The second communications device may wait an SIFSduration to respond to the first communications device with anacknowledgement frame after receiving the synchronization frame.

Optionally, for a schematic diagram of channel access in thesingle-device wake-up scenario, refer to FIG. 7.

2. A multi-device wake-up scenario: In this scenario, there are a numberof woken-up second communications devices. Before MRs of the number ofsecond communications devices go to sleep, each second communicationsdevice sends a channel synchronization request to the firstcommunications device. In a phase, the MRs of the second communicationsdevices enter a sleep state, and the first communications device sends amulti-device WUP to WURs of the second communications devices, totrigger the MRs of the second communications devices to wake up. Themulti-device WUP carries identifiers of the second communicationsdevices. After the first communications device receives the channelsynchronization request and learns that the MRs of the secondcommunications devices have woken up (as described above, a wake-upmoment herein is a time estimated or specified by the firstcommunications device, but not notified by the second communicationsdevice), the first communications device sends a synchronization frameto trigger the MRs of the second communications devices to access achannel without waiting for a probe delay time.

In this scenario, the first communications device may send, when thechannel is idle, the synchronization frame to the second communicationsdevices in the following five sending manners (1), (2), (3), (4), and(5).

(1) The first communications device sends, when the channel is idle, afirst synchronization frame to any one of the woken-up secondcommunications devices, where the first synchronization frame carries anidentifier of the any one woken-up second communications device, and thefirst synchronization frame is used to instruct the any one woken-upsecond communications device to wait first preset duration to access thechannel after receiving the first synchronization frame.

In an exemplary implementation, there are the number of woken-up secondcommunications devices, and the first communications device may send thefirst synchronization frame to any one second communications device (itis assumed that the second communications device is a device A) in thenumber of woken-up second communications devices, where the firstsynchronization frame may carry an identifier of the device A.Optionally, the identifier may be an identifier of a WUR of the deviceA, or may be an association identifier of the device A. The firstsynchronization frame is used to instruct the device A to wait the firstpreset duration to access the channel after receiving the firstsynchronization frame sent by the first communications device.Optionally, the first preset duration may be an SIFS duration. It shouldbe noted that, in this implementation, the first communications deviceneeds to send the first synchronization frame to only one woken-upsecond communications device and does not need to send a correspondingsynchronization frame to other second communications devices. Atransmission time of the synchronization frame can be reduced, and theother second communications devices can access the channel withoutwaiting for a probe delay time, since the first communications devicehas sent the first synchronization frame to the device A. In this case,the other second communications devices may detect that the frame isbeing transmitted on the channel Therefore, the other secondcommunications devices only need to wait until NAVs of the other secondcommunications devices decrease to 0, to preempt the channel to senddata. The other second communications devices do not need to wait forthe probe delay time (for example, the second communications device is astation, and there are two cases in which the station wakes up fromsleep. In one case, an MR of the station wakes up and does not detectthat a frame is being transmitted on a channel. Therefore, the stationneeds to wait the probe delay time to preempt the channel to send data.In another case, an MR of the station wakes up and detects that a frameis being transmitted on a channel. In this case, the station only needsto wait until a NAV of the station decreases to 0, to access thechannel). In addition, the first communications device does not need tosend another synchronization frame. Therefore, this reduces thetransmission time of the synchronization frame, and also ensures thatthe other second communications devices can quickly access the channel.

Optionally, the first synchronization frame may be the CTS frame, theRTS frame, or the trigger frame. The CTS frame, the RTS frame, and thetrigger frame each may carry the identifier of the any one woken-upsecond communications device. For example, a receiver address of thetrigger frame is set to an address of the woken-up second communicationsdevice. The trigger frame in Table 5 includes a user information field.It should be noted that the identifier of the second communicationsdevice that is carried in each of the CTS frame, the RTS frame, and thetrigger frame is an explicit identifier of the second communicationsdevice, for example, an identifier or an association identifier of theWUR of the second communications device. In other words, the identifierof the second communications device can explicitly indicate the secondcommunications device that accesses the channel, to accelerateassistance in channel synchronization.

(2) The first communications device sends, when the channel is idle, asecond synchronization frame to the number of woken-up secondcommunications devices, where the second synchronization frame is usedto instruct each woken-up second communications device to wait a secondpreset duration to perform a backoff procedure to contend for access tothe channel after receiving the second synchronization frame, and areceiver address of the second synchronization frame is a broadcastaddress.

In this implementation, there are the number of woken-up secondcommunications devices, and the first communications device sends thesecond synchronization frame to the number of woken-up secondcommunications devices, where the receiver address of the secondsynchronization frame is the broadcast address. Therefore, each woken-upsecond communications device may receive the second synchronizationframe, and wait the second preset duration (the channel is idle in thesecond preset duration) to perform the backoff procedure to contend foraccess to the channel after receiving the second synchronization frame.The second preset duration may be DIFS, or the second preset durationmay be any other duration. It should be noted that the secondsynchronization frame does not carry an identifier of each woken-upsecond communications device.

Optionally, the second synchronization frame may be a CTS frame, the RTSframe, or the CF-end frame. A difference between the CTS frame and theRTS frame in the single-device wake-up, and the CTS frame and the RTSframe is that receiver addresses of the CTS frame and the RTS frame eachare a broadcast address. A receiver address of the CF-end frame is alsoa broadcast address.

(3) The first communications device sends, when the channel is idle, athird synchronization frame to the number of woken-up secondcommunications devices, where the third synchronization frame carries asub-channel resource indication of each woken-up second communicationsdevice and an identifier of each woken-up second communications device;a receiver address of the third synchronization frame is a broadcastaddress; and the third synchronization frame is used to instruct thenumber of woken-up second communications devices to wait first presetduration to simultaneously access the channel based on their respectivesub-channel resource indications after receiving the thirdsynchronization frame.

In this implementation, there are a number of woken-up secondcommunications devices, and the first communications device sends thethird synchronization frame to the woken-up second communicationsdevices, where the receiver address of the third synchronization frameis the broadcast address. Therefore, each woken-up second communicationsdevice may receive the third synchronization frame. In addition, thethird synchronization frame carries the sub-channel resource indicationof each woken-up second communications device and the identifier of eachwoken-up second communications device. Therefore, each woken-up secondcommunications device accesses, with reference to the sub-channelresource indication corresponding to each woken-up second communicationsdevice in the third synchronization frame, the channel on acorresponding sub-channel resource after receiving the thirdsynchronization frame. The woken-up second communications devices maywait the first preset duration to simultaneously perform uplinkmultiplexing transmission such as orthogonal frequency division multipleaccess (OFDMA) transmission or multi-user multiple-input multiple-output(MU-MIMO) transmission to simultaneously access the channel afterreceiving the third synchronization frame. The first preset durationherein may be an SIFS time, or may be other duration less than the probedelay time.

Optionally, the third synchronization frame may be a multi-user CTSframe, a multi-user RTS frame, or a trigger frame. A difference from theCTS frame, the RTS frame, or the trigger frame in (1) and (2) is thatreceiver addresses of the multi-user CTS frame, the multi-user RTSframe, and the trigger frame each are a broadcast address. In addition,the multi-user CTS frame, the multi-user RTS frame, and the triggerframe each carry the identifier of each woken-up second communicationsdevice and the sub-channel resource indication of each woken-up secondcommunications device. The trigger frame is used as an example. Withreference to the structure of the trigger frame in Table 5, the triggerframe includes a number of user information fields, and the number ofwoken-up second communications devices simultaneously transmit wake-upreport frames by using OFDMA or MU-MIMO based on sub-channel resourceindications in the trigger frame.

In this implementation, the number of woken-up second communicationsdevices may be simultaneously scheduled by using the thirdsynchronization frame, thereby improving channel access efficiency ofthe woken-up second communications devices.

(4) The first communications device sends, when the channel is idle, anL-Preamble to the woken-up second communications devices, where theL-Preamble carries first indication information and all or a portion ofbits of a check code field of a WUP that is received by the WURs of thewoken-up second communications devices to wake up main transceivers ofthe number of second communications devices; the first indicationinformation is used to indicate, to the woken-up second communicationsdevices, that the L-Preamble is a synchronization frame; the all or theportion of bits of the check code field are used to indicate identifiersof the woken-up second communications devices; and the L-Preamble isused to instruct the woken-up second communications devices to waitsecond preset duration to perform a backoff procedure to contend foraccess to the channel after receiving the L-Preamble.

In this implementation, the synchronization frame is the L-Preamble thatcarries the first indication information and the all or the portion ofbits of the check code field of the WUP. The WUP herein is a WUP used towake up the main transceivers of the number of second communicationsdevices. The first indication information is used to indicate, to thewoken-up second communications devices, that the L-Preamble is asynchronization frame, and the all or the portion of bits of the checkcode field of the WUP are used to indicate the identifiers of thewoken-up second communications devices. When the first communicationsdevice sends the L-Preamble, that is, sends the L-Preamble to thewoken-up second communications devices, the woken-up secondcommunications devices wait the second preset duration to perform thebackoff procedure to contend for access to the channel after receivingthe L-Preamble. The second preset duration may be DIFS, or any otherduration. If the channel is idle within the second preset duration, thewoken-up second communications devices perform the backoff procedure tocontend for access to the channel. For example, the woken-up secondcommunications devices send wake-up report frames to the firstcommunications device.

Optionally, in the multi-device wake-up scenario, when an implementationof the synchronization frame is (2) or (3), for a schematic diagram ofaccessing a channel by a woken-up second communications device, refer toFIG. 8.

(5) The first communications device may send, one by one when thechannel is idle, a synchronization frame to the number of woken-upsecond communications devices, where the synchronization frame sent toeach woken-up second communications device carries first indicationinformation and an identifier of a corresponding woken-up secondcommunications device. A simple example is used herein to brieflydescribe a process of “sending one by one”.

It is assumed that there are stations A, B, C, and D. When an AP wakesup a number of stations, a WUP sent by the AP includes identifiers ofthe four stations. It is assumed that the identifiers of the stations inthe WUP are sequentially an identifier of the station A, an identifierof the station B, an identifier of the station C, and an identifier ofthe station D. A is a station that ranks first, and B, C, and D arestations that rank second, third, and fourth, respectively. In addition,it is assumed that A, B, and C are stations that have a channelsynchronization requirement (before MRs go to sleep, the stations A, B,and C each send a channel synchronization request to the AP, to requestthe AP to assist the stations A, B, and C in quickly accessing a channelwithout waiting for a probe delay time), and D is a station that doesnot have a channel synchronization requirement.

During sending, the AP first sends a synchronization frame to thestation A (or any specified station), and then the station A waits anSIFS time to return a wake-up report frame to the AP after receiving thesynchronization frame. Next, the AP continues to send thesynchronization frame to the station B, and the station B waits an SIFSduration to return a wake-up report frame to the AP after receiving thesynchronization frame. Then, the AP sends the synchronization frame tothe station C, and the station C waits the SIFS duration to return awake-up report frame to the AP after receiving the synchronizationframe. In addition, because the station D does not send a channelsynchronization request to the AP, the AP does not need to send asynchronization frame to the station D, and the station D needs to waitthe probe delay time to preempt the channel to send a wake-up reportframe.

In the case in which the first communications device sends thesynchronization frames one by one, the synchronization frame may be theL-Preamble, the CTS frame, the RTS frame, or the trigger frame.

In conclusion, regardless of the single-device wake-up scenario or themulti-device wake-up scenario, provided that the second communicationsdevice sends the channel synchronization request to the firstcommunications device before the second communications device goes tosleep, the first communications device sends, when the channel is idleand with reference to the time at which the second communications deviceis woken up and that is learned by the first communications device, thesynchronization frame to the woken-up second communications device totrigger the woken-up second communications device to access the channelwithout waiting for the probe delay time, thereby reducing a waitingtime of the MR of the woken-up second communications device, andreducing power consumption of the second communications device. Inaddition, the first communications device sends the firstsynchronization frame to any one of the number of woken-up secondcommunications devices, to trigger the second communications devices toaccess the channel without waiting for the probe delay time. Thisgreatly reduces a transmission time of the synchronization frame, andalso ensures that the woken-up second communications devices can quicklyaccess the channel.

FIG. 9 is a schematic structural diagram of an embodiment of a channelaccess indication apparatus. The channel access indication apparatus maybe integrated into the first communications device in the foregoingmethod embodiment, or may be the first communications device. Theindication apparatus may be implemented by software, hardware, or acombination of software and hardware. As shown in FIG. 9, the apparatusincludes a receiving module 11, a processing module 12, and a sendingmodule 13.

The receiving module 11 is configured to receive a channelsynchronization request sent by a second communications device, thechannel synchronization request is used to request the firstcommunications device to send a synchronization frame to the secondcommunications device, and a WUR is configured for the secondcommunications device.

The processing module 12 is configured to: according to the channelsynchronization request and a time at which the second communicationsdevice is woken up and that is learned by the first communicationsdevice based on preset signaling, instruct the sending module 13 tosend, when a channel is idle, the synchronization frame to the woken-upsecond communications device, and the synchronization frame is used toinstruct the woken-up second communications device to access the channelafter receiving the synchronization frame.

Optionally, if there are a number of woken-up second communicationsdevices, the sending module 13 is configured to send, when the channelis idle, a first synchronization frame to any one of the number ofwoken-up second communications devices, where the first synchronizationframe carries an identifier of the any one woken-up secondcommunications device; and the first synchronization frame is used toinstruct the any one woken-up second communications device to wait firstpreset duration to access the channel after receiving the firstsynchronization frame. The first synchronization frame is a CTS frame,an RTS frame, or a trigger frame.

Optionally, if there are a number of woken-up second communicationsdevices, the sending module 13 is configured to send, when the channelis idle, a second synchronization frame to the woken-up secondcommunications devices, where the second synchronization frame is usedto instruct each woken-up second communications device to wait secondpreset duration to perform a backoff procedure to contend for access tothe channel after receiving the second synchronization frame; and areceiver address of the second synchronization frame is a broadcastaddress. The second synchronization frame is a CTS frame, an RTS frame,or a CF-end frame.

With reference to the foregoing two optional manners, the CTS frame maycarry second indication information; and the second indicationinformation is used to indicate, to the woken-up second communicationsdevice, that the CTS frame is a synchronization frame.

Optionally, if there are a number of woken-up second communicationsdevices, the sending module 13 is configured to send, when the channelis idle, a third synchronization frame to the woken-up secondcommunications devices, where the third synchronization frame carries asub-channel resource indication of each woken-up second communicationsdevice and an identifier of each woken-up second communications device;a receiver address of the third synchronization frame is a broadcastaddress; and the third synchronization frame is used to instruct thewoken-up second communications devices to wait first preset duration tosimultaneously access the channel based on their respective sub-channelresource indications after receiving the third synchronization frame.The third synchronization frame is a multi-user CTS frame, a multi-userRTS frame, or a trigger frame.

Optionally, if there are a number of woken-up second communicationsdevices, the sending module 13 is configured to send, when the channelis idle, an L-Preamble to the woken-up second communications devices,where the L-Preamble carries first indication information and all or aportion of bits of a check code field of a WUP that is received by WURsof the number of woken-up second communications devices to wake up maintransceivers of the number of second communications devices; the firstindication information is used to indicate, to the woken-up secondcommunications devices, that the L-Preamble is a synchronization frame;the all or the portion of bits of the check code field are used toindicate identifiers of the woken-up second communications devices; andthe L-Preamble is used to instruct the woken-up second communicationsdevices to wait a second preset duration to perform a backoff procedureto contend for access to the channel after receiving the L-Preamble.

Optionally, if there is one woken-up second communications device, thesynchronization frame is an L-Preamble, where the L-Preamble carriesfirst indication information and all or a portion of bits of a checkcode field of a WUP received by a WUR of the woken-up secondcommunications device; the first indication information is used toindicate, to the second communications device, that the L-Preamble is asynchronization frame; and the all or the portion of bits of the checkcode field are used to indicate an identifier of the woken-up secondcommunications device.

Optionally, if there is one woken-up second communications device, thesynchronization frame is any one of a CTS frame, an RTS frame, or atrigger frame, and the synchronization frame carries an identifier ofthe woken-up second communications device.

Optionally, the first preset duration is an SIFS period.

Optionally, the second preset duration is a DIFS.

Optionally, the receiving module 11 is configured to receive anassociation request frame sent by the second communications device,where the association request frame carries indication information ofthe channel synchronization request of the second communications device.

Optionally, the receiving module 11 is configured to receive amanagement frame or a control frame sent by the second communicationsdevice, where the management frame or the control frame carriesindication information of the channel synchronization request.

The channel access indication apparatus may execute an embodiment of theforegoing method. An implementation principle and a technical effect ofthe channel access indication apparatus are similar. Details are notdescribed herein again.

FIG. 10 is a schematic structural diagram of an embodiment of a channelaccess indication device. The channel access indication device may bethe first communications device. As shown in FIG. 10, the firstcommunications device includes a receiver 20, a memory 21, a processor22, a transmitter 23, and at least one communications bus 24. Thecommunications bus 24 is configured to implement a communicationconnection between elements. The memory 21 may include a high-speed RAMmemory, or may include a nonvolatile memory (NVM), for example, at leastone magnetic disk memory. The memory 21 may store various programs, usedto complete various processing functions and implement steps of themethod in this embodiment.

In an exemplary embodiment, the receiver 20 is configured to receive achannel synchronization request sent by a second communications device,the channel synchronization request is used to request the firstcommunications device to send a synchronization frame to the secondcommunications device, and a WUR is configured for the secondcommunications device.

The processor 22 is configured to: according to the channelsynchronization request and a time at which the second communicationsdevice is woken up and that is learned by the first communicationsdevice based on preset signaling, instruct the transmitter 23 to send,when a channel is idle, the synchronization frame to the woken-up secondcommunications device, and the synchronization frame is used to instructthe woken-up second communications device to access the channel afterreceiving the synchronization frame.

Optionally, if there are a number of woken-up second communicationsdevices, the transmitter 23 is configured to send, when the channel isidle, a first synchronization frame to any one of the woken-up secondcommunications devices, where the first synchronization frame carries anidentifier of the any one woken-up second communications device; and thefirst synchronization frame is used to instruct the any one woken-upsecond communications device to wait first preset duration to access thechannel after receiving the first synchronization frame. The firstsynchronization frame is a CTS frame, an RTS frame, or a trigger frame.

Optionally, if there are a number of woken-up second communicationsdevices, the transmitter 23 is configured to send, when the channel isidle, a second synchronization frame to the woken-up secondcommunications devices, where the second synchronization frame is usedto instruct each woken-up second communications device to wait secondpreset duration to perform a backoff procedure to contend for access tothe channel after receiving the second synchronization frame; and areceiver address of the second synchronization frame is a broadcastaddress. The second synchronization frame is a CTS frame, an RTS frame,or a CF-end frame.

With reference to the foregoing two optional manners, the CTS frame maycarry second indication information; and the second indicationinformation is used to indicate, to the woken-up second communicationsdevice, that the CTS frame is a synchronization frame.

Optionally, if there are a number of woken-up second communicationsdevices, the transmitter 23 is configured to send, when the channel isidle, a third synchronization frame to the woken-up secondcommunications devices, where the third synchronization frame carries asub-channel resource indication of each woken-up second communicationsdevice and an identifier of each woken-up second communications device;a receiver address of the third synchronization frame is a broadcastaddress; and the third synchronization frame is used to instruct thewoken-up second communications devices to wait first preset duration tosimultaneously access the channel based on their respective sub-channelresource indications after receiving the third synchronization frame.The third synchronization frame may be a multi-user CTS frame, amulti-user RTS frame, or a trigger frame.

Optionally, if there are a number of woken-up second communicationsdevices, the transmitter 23 is configured to send, when the channel isidle, an L-Preamble to the woken-up second communications devices, wherethe L-Preamble carries first indication information and all or a portionof bits of a check code field of a WUP that is received by WURs of thewoken-up second communications devices to wake up main transceivers ofthe second communications devices; the first indication information isused to indicate, to the woken-up second communications devices, thatthe L-Preamble is a synchronization frame; the all or the portion ofbits of the check code field are used to indicate identifiers of thewoken-up second communications devices; and the L-Preamble is used toinstruct the woken-up second communications devices to wait a secondpreset duration to perform a backoff procedure to contend for access tothe channel after receiving the L-Preamble.

Optionally, if there is one woken-up second communications device, thesynchronization frame is an L-Preamble, where the L-Preamble carriesfirst indication information and all or a portion of bits of a checkcode field of a WUP received by a WUR of the woken-up secondcommunications device; the first indication information is used toindicate, to the second communications device, that the L-Preamble is asynchronization frame; and the all or the portion of bits of the checkcode field are used to indicate an identifier of the woken-up secondcommunications device.

Optionally, if there is one woken-up second communications device, thesynchronization frame is a CTS frame, an RTS frame, or a trigger frame,and the synchronization frame carries an identifier of the woken-upsecond communications device.

Optionally, the first preset duration is an SIFS period.

Optionally, the second preset duration is a DIFS.

Optionally, the receiver 20 is configured to receive an associationrequest frame sent by the second communications device, where theassociation request frame carries indication information of the channelsynchronization request of the second communications device.

Optionally, the receiver 20 is configured to receive a management frameor a control frame sent by the second communications device, where themanagement frame or the control frame carries indication information ofthe channel synchronization request.

The channel access indication device may execute an embodiment of theforegoing method. An implementation principle and a technical effect ofthe channel access indication device are similar. Details are notdescribed herein again.

Methods or algorithm steps described with reference to the contentdisclosed herein may be implemented by hardware, or may be implementedby a processor by executing a software instruction, or may beimplemented by using a computer program product. The softwareinstruction may include a corresponding software module. The softwaremodule may be located in a RAM memory, a flash memory, a ROM memory, anEPROM memory, an EEPROM memory, a register, a hard disk, a removablehard disk, a CD-ROM, or a storage medium of any other form well-known inthe art. For example, a storage medium is coupled to the processor, sothat the processor can read information from the storage medium andwrite information into the storage medium. The storage medium mayalternatively be a component of the processor. The processor and thestorage medium may be located in an ASIC. In addition, the ASIC may belocated in user equipment. The processor and the storage medium mayexist in the user equipment as discrete components.

A person of ordinary skill in the art should understand that in theforegoing one or more examples, the functions may be implemented byhardware, software, firmware, or any combination thereof. When thefunctions are implemented by software, the functions may be stored in acomputer-readable medium or transmitted as one or more instructions orcode in a computer-readable medium. The computer-readable mediumincludes a computer storage medium and a communications medium, wherethe communications medium includes any medium that enables a computerprogram to be transmitted from one place to another. The storage mediummay be any available medium accessible to a general-purpose or dedicatedcomputer.

In the several exemplary embodiments provided herein, it should beunderstood by a person of ordinary skill in the art that the disclosedsystem, device, and method may be implemented in other manners withoutdeparting from the scope of the embodiments. For example, theembodiments described above are merely examples. For example, divisionof the modules or units is merely logical function division, and theremay be another division manner in actual implementation. For example, anumber of units or components may be combined or integrated into anothersystem, or some features may be ignored or not performed. The unitsdescribed as separate parts may or may not be physically separate, andparts displayed as units may or may not be physical units, and may belocated in one position, or may be distributed on a number of networkunits. Some or all of the modules may be selected based on an actualrequirement to achieve the objectives of the solutions of theembodiments.

In addition, the described system, device, and method, and schematicdiagrams of different embodiments may be combined or integrated withother systems, modules, technologies, or methods without departing fromthe scope of the embodiments. In addition, the displayed or discussedmutual couplings or direct couplings or communication connections may beimplemented by using some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electronic, mechanical, or another form.

What is claimed is:
 1. A channel access indication method, comprising:receiving, by a first communications device, a channel synchronizationrequest sent by a second communications device, wherein the channelsynchronization request requests the first communications device to senda synchronization frame to the second communications device, and awake-up receiver is configured for the second communications device; andaccording to the channel synchronization request and a time at which thesecond communications device is woken up and that is learned by thefirst communications device based on preset signaling, sending, by thefirst communications device when a channel is idle, the synchronizationframe to the woken-up second communications device, wherein thesynchronization frame instructs the woken-up second communicationsdevice to access the channel after receiving the synchronization frame,wherein there are a plurality of woken-up second communications devices,and the synchronization frame is sent in response to the channelsynchronization request based on the time at which the secondcommunications device is woken up, and the synchronization frame carriespredetermined information including an identifier of the one or morewoken-up second communications device, wherein the sending, when achannel is idle, of the synchronization frame to the woken-up secondcommunications device comprises: sending, by the first communicationsdevice when the channel is idle, a first synchronization frame to one ormore of the plurality of woken-up second communications devices; andsending, by the first communications device when the channel is idle, asecond synchronization frame to the plurality of woken-up secondcommunications devices, wherein the first synchronization frame includesthe identifier of the one or more woken-up second communications device,and the second synchronization frame does not include the identifier,wherein a receiver address of the second synchronization frame is abroadcast address.
 2. The method according to claim 1, wherein the firstsynchronization frame instructs the one or more woken-up secondcommunications device to wait a first preset duration to access thechannel after receiving the first synchronization frame, and the firstpreset duration is a short inter-frame space (SIFS).
 3. The methodaccording to claim 1, wherein the second synchronization frame instructseach woken-up second communications device to wait a second presetduration to perform a backoff procedure to contend for access to thechannel after receiving the second synchronization frame, and the secondpreset duration is a distributed coordination function inter-frame space(DIFS).
 4. The method according to claim 1, wherein the sending, when achannel is idle, of the synchronization frame to the woken-up secondcommunications device further comprises: sending, by the firstcommunications device when the channel is idle, a third synchronizationframe to the plurality of woken-up second communications devices,wherein the third synchronization frame carries a sub-channel resourceindication of each woken-up second communications device and theidentifier of each woken-up second communications device; a receiveraddress of the third synchronization frame is a broadcast address; andthe third synchronization frame instructs the plurality of woken-upsecond communications devices to wait a first preset duration tosimultaneously access the channel based on their respective sub-channelresource indications after receiving the third synchronization frame. 5.The method according to claim 1, wherein the sending, when a channel isidle, of the synchronization frame to the woken-up second communicationsdevice further comprises: sending, by the first communications devicewhen the channel is idle, a physical layer legacy preamble L-Preamble tothe plurality of woken-up second communications devices, wherein theL-Preamble carries first indication information and all or a portionbits of a check code field of a wake-up frame that is received bywake-up receivers of the plurality of woken-up second communicationsdevices to wake up main transceivers of the plurality of secondcommunications devices; the first indication information indicates, tothe plurality of woken-up second communications devices, that theL-Preamble is a synchronization frame; the all or the portion bits ofthe check code field indicate the identifiers of the plurality ofwoken-up second communications devices; and the L-Preamble instructs theplurality of woken-up second communications devices to wait a secondpreset duration to perform a backoff procedure to contend for access tothe channel after receiving the L-Preamble.
 6. The method according toclaim 1, wherein the synchronization frame further includes a physicallayer legacy preamble L-Preamble, wherein the L-Preamble carries firstindication information and all or a portion bits of a check code fieldof a wake-up frame received by a wake-up receiver of the woken-up secondcommunications device; the first indication information indicates, tothe second communications device, that the L-Preamble is asynchronization frame; and the all or the portion bits of the check codefield indicate the identifier of the woken-up second communicationsdevice.
 7. The method according to claim 1, the synchronization framefurther includes any one of a clear-to-send CTS frame, a request-to-sendRTS frame, or a trigger frame; and the synchronization frame carries theidentifier of the woken-up second communications device.
 8. The methodaccording to claim 1, wherein the first synchronization frame is any oneof a clear-to-send (CTS) frame, a request-to-send (RTS) frame, or atrigger frame.
 9. The method according to claim 1, wherein thereceiving, by a first communications device, of the channelsynchronization request sent by a second communications devicecomprises: receiving, by the first communications device, an associationrequest frame sent by the second communications device, wherein theassociation request frame carries indication information of the channelsynchronization request of the second communications device.
 10. Themethod according to claim 1, wherein the receiving, by a firstcommunications device, of the channel synchronization request sent by asecond communications device comprises: receiving, by the firstcommunications device, a management frame or a control frame sent by thesecond communications device or a control frame sent by the secondcommunications device, wherein the management frame or the control framecarries indication information of the channel synchronization request.11. A channel access indication device comprising: a firstcommunications device, the first communications device comprising: areceiver configured to receive a channel synchronization request sent bya second communications device, the channel synchronization requestrequests the first communications device to send a synchronization frameto the second communications device, and a wake-up receiver isconfigured for the second communications device; and a processorconfigured to: according to the channel synchronization request and atime at which the second communications device is woken up and that islearned by the first communications device based on preset signaling,instruct a transmitter to send, when a channel is idle, thesynchronization frame to the woken-up second communications device, andthe synchronization frame instructs the woken-up second communicationsdevice to access the channel after receiving the synchronization frame,wherein there are a plurality of woken-up second communications devices,and the synchronization frame is sent in response to the channelsynchronization request based on the time at which the secondcommunications device is woken up, and the synchronization frame carriespredetermined information including an identifier of the one or morewoken-up second communications device, wherein when the channel is idle,the transmitter is configured to send: a first synchronization frame toone or more of the plurality of woken-up second communications devices;and a second synchronization frame to the plurality of woken-up secondcommunications devices, wherein the first synchronization frame includesthe identifier of the one or more woken-up second communications device,and the second synchronization frame does not include the identifier,wherein a receiver address of the second synchronization frame is abroadcast address.
 12. The device according to claim 11, wherein thereceiver is configured to receive a management frame or a control framesent by the second communications device, and the management frame orthe control frame carries indication information of the channelsynchronization request.
 13. The device according to claim 11, the firstsynchronization frame instructs the one or more woken-up secondcommunications devices to wait a first preset duration to access thechannel after receiving the first synchronization frame, and the firstpreset duration is a SIFS.
 14. The device according to claim 11, whereinthe second synchronization frame instructs each woken-up secondcommunications device to wait a second preset duration to perform abackoff procedure to contend for access to the channel after receivingthe second synchronization frame, and the second preset duration is aDIFS.
 15. The device according to claim 11, wherein the transmitter isfurther configured to send, when the channel is idle, a thirdsynchronization frame to the plurality of woken-up second communicationsdevices, wherein the third synchronization frame carries a sub-channelresource indication of each woken-up second communications device andthe identifier of each woken-up second communications device; a receiveraddress of the third synchronization frame is a broadcast address; andthe third synchronization frame instructs the plurality of woken-upsecond communications devices to wait a first preset duration tosimultaneously access the channel based on their respective sub-channelresource indications after receiving the third synchronization frame.16. The device according to claim 11, wherein the transmitter is furtherconfigured to send, when the channel is idle, a physical layer legacypreamble L-Preamble to the plurality of woken-up second communicationsdevices, wherein the L-Preamble carries first indication information andall or a portion bits of a check code field of a wake-up frame that isreceived by wake-up receivers of the plurality of woken-up secondcommunications devices to wake up main transceivers of the plurality ofsecond communications devices; the first indication informationindicates, to the plurality of woken-up second communications devices,that the L-Preamble is a synchronization frame; the all or the portionbits of the check code field indicate the identifiers of the pluralityof woken-up second communications devices; and the L-Preamble instructsthe plurality of woken-up second communications devices to wait secondpreset duration to perform a backoff procedure to contend for access tothe channel after receiving the L-Preamble.
 17. The device according toclaim 11, wherein the synchronization frame further includes a physicallayer legacy preamble L-Preamble, wherein the L-Preamble carries firstindication information and all or a portion bits of a check code fieldof a wake-up frame received by a wake-up receiver of the woken-up secondcommunications device; the first indication information indicates, tothe second communications device, that the L-Preamble is asynchronization frame; and the all or the portion bits of the check codefield indicate the identifier of the woken-up second communicationsdevice.
 18. The device according to claim 11, wherein thesynchronization frame further includes any one of a clear-to-send (CTS)frame, a request-to-send (RTS) frame, or a trigger frame, and thesynchronization frame carries the identifier of the woken-up secondcommunications device.
 19. The device according to claim 11, wherein thefirst synchronization frame is any one of a clear-to-send (CTS) frame, arequest-to-send (RTS) frame, or a trigger frame.
 20. The deviceaccording to claim 11, wherein the receiver is configured to receive anassociation request frame sent by the second communications device, andthe association request frame carries indication information of thechannel synchronization request of the second communications device.